The invention relates to a structure for the shielding of electronic components arranged on a printed circuit board from outside electromagnetic fields.
U.S. Pat. No. 4,945,323 describes a structure of this type comprising a shielding housing, which defines a first chamber exposed to electromagnetic fields and a shielded second chamber. Electric conductor means extend to electronic components in the first chamber. A multi-layer printed circuit board is provided with outer surfaces and an internal, grounded conductive coating. The conductor means include through-contacts passing through the multi-layer printed circuit board.
Sensitive electronic devices such as flight or engine computer of aircraft are arranged in a chamber shielded from electromagnetic fields. Electric connecting lines are lead to these devices. The connecting lines come from a space in which strong electric or magnetic fields of high frequency can be present. The connecting lines carry intelligence signals. These intelligence signals may be analog signals or digital pulse sequences. Interfering electromagnetic fields may reach the shielded chamber or space through these connecting lines. Then signals which are superimposed to the inteligence signals may be induced in the connecting lines and may saturate and "clog" the signal processing.
Therefore U.S. Pat. No. 4,945,323 provides a filter arrangement for filtering a plurality of connecting lines, which extend from a space containing electromagnetic fields through a multi-layer printed circuit board to a device located in a shielded chamber. The printed circuit board has a continuous, internal, grounded coating. As signal lead-through means, the grounded conductive coating has narrow apertures through which through-contacts extend at a small distance from the edges of the apertures. Electrically conductive coatings on those layers which are adjacent to the grounded conductive coating form filter capacitors with this grounded conductive coating. The conductive coatings on are connected with the through-contacts. Filter components in the form of SMD-components are mounted on the printed circuit board. The grounded, conducting coating extends to the edges of the printed circuit board . The edges of the printed circuit board are copper-plated all around and are well conductively connected with the housing.
In the structure of U.S. Pat. No. 4,945,323, the printed circuit board serves exclusively as a partition, which separates a "polluted" chamber containing electromagnetic fields from a shielded "clean" chamber.